1. Field of the Invention
The present invention relates to a tape cartridge, and more particularly to a tape cartridge housing a metal recording medium such as a magnetic recording tape.
2. Description of the Prior Art
FIGS. 1 to 6 show an example of a conventional tape cartridge, wherein a case body 1 is formed by assembling a top case half 1a and a bottom case half 1b made of plastic resin material together so that a pair of tape reels 3 are rotatably installed in the left and right portions of the case body 1. There is defined a pair of tape drawing openings 4 at the side end portions or left and right end portions in the front face of the case body 1. A pocket 5 for the tape loading is defined at the central portion of the case body in such a manner that the pocket 5 is expanded towards the inside of the case body 1 between the left and right tape drawing openings 4. In this arrangement, the magnetic tape 2 is taken out of one of the tape reels 3 through the tape drawing opening facing to the tape reel 3 which releases the recording tape, and the released tape is advanced toward the front side of the pocket 3, then introduced in the other tape drawing opening and taken up by the other tape reel 3 in a known manner.
A front lid 6 is mounted on the front part of the case body 1 for covering and protecting the front surface or recording surface of the magnetic tape 2 extending between the tape drawing openings 4. The front lid 6 is made of plastic resin and comprises a front wall 6a extending in a lateral direction so as to close the entire length of the front part of the case body 1, side arms 6b projected backward of the case body from both side ends of the front wall 6a and pivotal shafts 7 projected from the inner surfaces of the side arms 6b. The front lid 6 is pivotally mounted on both side walls 8 of the case body 1 by rotatably engaging the pivotal shafts 7 in recesses defined in the side walls 8, so that the front lid 6 is movable between a closed position or down position at which the front lid 6 covers the front face of the magnetic tape 2 as shown in the real line in FIG. 3 and up position or open position at which the front side of the magnetic tape 2 is opened, as shown in chain lines in FIG. 3. The front lid 6 is normally exerted toward the closed position by a resilient member (not shown) engaged with one of the pivotal shafts 7.
There is provided a rear lid 11 on the rear side of the front lid 6 in the area where the pocket 5 for the tape loading is defined. When the tape cartridge is not used, the rear lid 11 covers the rear surface of the magnetic tape 2, more specifically the rear lid 11 covers the inner side as well as the lower part of the magnetic tape 2 and the upper opened part of the pocket 5.
The rear lid 11 is made of plastic resin and is formed by molding with a generally T character shape in a cross sectional view, as shown in FIG. 3. The rear lid 11 comprises a slanted wall 12 for covering the rear face of the the magnetic tape 2, a top wall 13 projected from the top edge of the slanted wall 2 for covering the upper opening of the pocket 5, a pair of pivotal shafts 14 projected from the central area of both side edges 11a and 11b of the slanted wall 12 and a pair of sliding shafts 15 provided at the portions lower than the pivotal shafts 14 of the side edges 11a and 11b. The pivotal shafts 14 are rotatably engaged with the shaft supporting members 16 projected backward from the rear surface of the front lid 6 with the sliding shafts 15 slidably engaged in S shaped guide slots 18a and 18b which are respectively defined on the inner surface of the rear lid guide walls 5a and 5b in the pocket 5. The guide slots 18a and 18b are formed by assembling the guide walls 5a and 5b of the top case half 1a and the bottom case half 1b, as shown in FIG. 4.
The front lid 6 and the rear lid 11 can be opened upward from the closed position shown in the real line in FIG. 3. That is, when the front lid 6 is moved upward to its open position from the closed position, the rear lid 11 is also rotated with the movement of the front lid 6 around the pivotal shafts 14 and moved upward along the guide slots 18a and 18b, being opened upward as shown in the chain lines A in FIG. 3.
In the conventional tape cartridge as explained above, in order to facilitate the movement of the rear lid 11, there are defined clearances S between the lateral edges 11a and 11b of the rear lid 11 and rear lid guide walls 5a and 5b, as shown in FIGS. 5 and 6. Therefore, even when the rear lid 11 is in the closed position, a very small part of the magnetic tape 2 is visible directly from the outside of the case body 1 through the clearances S. Thus, harmful substance the air enters in the case body 1 through the clearances S and undesirably adheres to the magnetic tape 2 particularly the lower edge portion of the tape resulting in an undesired problem of corrosion of the magnetic tape 2 in case the magnetic tape is provided with a magnetic layer made of metallic material such as cobalt, cobalt-nickel, or cobalt phosphorus formed on a non magnetic substrate such as plastic resin film. It has been observed that in particular, such corrosion is apt to occur in the evaporated magnetic tape formed without binder.
Such harmful substances are sulfur, chlorine and other various floating substances of compounds or mist of sulfuric acid and nitric acid. Such harmful substance mentioned above is referred to as floating harmful particles hereinafter.